Burn DVD, but have slow down and freeze in spots

I have a Sony DVD Burner and have been able to make copies okay until recently. Now copied DVD has slow down spots and freeze spots. Is there something additional I need to overridw this problem? I use DVD Xpress and sometimes DVD Shrink 3.2 then to the sony DVD Decrypter.

Dont know about that LOL. Friend got this one with discount and couldnt refuse the buy. Ex: I copied Santa Claus 2 and I had slow spots and freeze. Then got another copy of it and it copied nicely. But the problem still there on most of the movies I cant understand why it started to do it.